A 4kW solar system typically costs between £5,500 and £7,000 installed, and a 6kW system between £8,500 and £10,500. The Energy Saving Trust puts the average UK home system at 4.5kWp costing around £7,600 (figures updated 21 July 2026). Bigger systems cost more upfront but generate more, so the size that pays back fastest is the one where you use most of the power yourself rather than exporting it.
This guide breaks the numbers down size by size: cost, panel count, roof space and yearly output. It sits alongside our full guide to solar panel costs in the UK, which covers VAT, grants and the Smart Export Guarantee in more detail.
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The table below sets out indicative installed cost, panel count, roof space and annual output for each common domestic size. The 4.5kWp row is the Energy Saving Trust's UK-wide benchmark; the other rows are typical quote ranges for a straightforward pitched-roof install, so a well-priced quote can sit below the EST average for the same size.
| System size | Typical installed cost | Panels | Roof space | Annual output |
|---|---|---|---|---|
| 3kWp | £4,500 – £5,500 | 7 – 8 | ~14 – 16 m² | 2,400 – 2,700 kWh |
| 4kWp | £5,500 – £7,000 | 9 – 11 | ~18 – 22 m² | 3,200 – 3,600 kWh |
| 4.5kWp (EST benchmark) | ~£7,600 | 10 – 12 | 20 – 30 m² | 3,600 – 4,050 kWh |
| 5kWp | £7,000 – £8,500 | 11 – 13 | ~24 – 26 m² | 4,000 – 4,500 kWh |
| 6kWp | £8,500 – £10,500 | 13 – 16 | ~28 – 32 m² | 4,800 – 5,400 kWh |
Panel counts assume 375W to 450W modules, so a system with higher-wattage panels needs fewer of them for the same kWp; roof space is roughly 2 m² per panel. Output uses the MCS methodology range of about 800 to 900+ kWh per kWp per year for a well-oriented UK roof, higher in southern England and lower in northern Scotland. Actual output depends on orientation, pitch, shading and location. Sources: Energy Saving Trust (system cost and typical size); MCS MIS 3002 standard (yield method).
3kWp: smaller homes and limited roof space
A 3kWp system costs around £4,500 to £5,500 and needs roughly 14 to 16 square metres of roof, or about 7 to 8 panels. It generates in the region of 2,400 to 2,700 kWh a year on a south-facing UK roof. This is the size to look at if you have a smaller roof, a mid-terrace with one usable pitch, or lower electricity use, for example a couple or a single-person household that is out during the day. It will not cover a home with an EV or a heat pump, but for a modest bill it is the cheapest way in.
4kWp: the popular choice for an average 3-bed house
A 4kW solar system typically costs £5,500 to £7,000 and needs about 18 to 22 square metres of roof, or 9 to 11 panels. It produces roughly 3,200 to 3,600 kWh a year, which is close to the annual electricity use of a typical three-bedroom home. This is the most-searched domestic size in the UK, and for good reason: it fits the roof of an average 1930s semi or a modern three-bed, and it broadly matches a family's yearly consumption. It stays comfortably within the 3.68kW-per-phase threshold for a simple G98 grid connection if the inverter is sized to suit, which our guide to G98 and G99 connections explains.
4.5kWp: the Energy Saving Trust benchmark
The Energy Saving Trust's reference system is 4.5kWp at around £7,600, using about 12 panels across 20 to 30 square metres of roof. That £7,600 is a UK-wide average that folds in difficult roofs, restricted access and scaffolding, which is why it sits above the typical 4kWp quote range for a straightforward install. If your roof is simple and south-facing, expect to be quoted below it; if it is a complex hipped or three-storey roof, the extra reflects real labour. The EST figure was last updated on 21 July 2026, and it moves, so always check it live against a current quote.
5kWp: four-bed homes and higher usage
A 5kWp system costs around £7,000 to £8,500 and needs roughly 24 to 26 square metres of roof, or 11 to 13 panels. It generates about 4,000 to 4,500 kWh a year. This is the size for a four-bedroom house, a family with high daytime use, or a home that is starting to add an electric car or an electric shower. The extra capacity only earns its keep if you use the surplus during the day or store it, because exported units are worth far less than the ones you avoid buying.
6kWp: large homes, EV charging and heat pumps
A 6kWp system costs around £8,500 to £10,500 and needs roughly 28 to 32 square metres of roof, or 13 to 16 panels. It produces about 4,800 to 5,400 kWh a year. This is the size to consider for a large detached home, a household charging an EV at home, or one running a heat pump, where electricity demand is high and much of it can be shifted into daylight hours. A system this size may push past 3.68kW per phase on a single-phase supply, which means the installer applies to the Distribution Network Operator under G99 before connecting, or fits an export limiter to stay within the simpler G98 route.
How to pick the right size for your home
Start with your annual electricity use, not your roof. Find your yearly kWh figure on a recent bill or in your online account, then match it to the output column above. A home using around 3,500 kWh a year is well served by a 4kWp to 4.5kWp system; one using 5,000 kWh or running an EV and a heat pump leans towards 5kWp or 6kWp.
Then check your roof. Multiply the number of panels by roughly 2 square metres to see whether the size you want actually fits your usable pitch, and remember that only the roof faces getting decent sun count. A south-facing pitch is ideal, but east-west splits work and simply spread generation across the day, which can suit a household that is home morning and evening.
Finally, think about when you use power. Solar pays back through self-consumption. Every unit you use as it is generated saves you the full import price, currently around 26p per kWh under the Ofgem price cap for 1 July to 30 September 2026. Every unit you export earns a Smart Export Guarantee rate of roughly 12p, and often less. So a bigger system that mostly exports pays back more slowly than a right-sized one you use yourself. Our guide to the Smart Export Guarantee rates covers what suppliers actually pay.
What each size saves and how long it takes to pay back
The Energy Saving Trust puts payback for a typical system at around 9 to 12 years with export payments, depending on where you live. Its July 2026 figures show roughly 9 years in London, 9 years in Aberystwyth, 10 years in Manchester and 11 years in Stirling, reflecting the difference in sunlight between the south and the north. Those periods assume you use a reasonable share of the electricity yourself. Sizing up does not automatically shorten payback: a larger system costs more and, unless you use or store the extra output, the surplus earns only the SEG export rate rather than the higher import price you avoid. This is why matching the system to your usage matters more than fitting the biggest array your roof allows. The full economics, including whether a battery changes the sums, are in our guide to whether solar panels are worth it in the UK and our solar battery storage costs guide.
Does VAT change with system size?
No. The 0% VAT rate on the supply and installation of solar panels applies whatever the system size, until 31 March 2027. After that it reverts to the 5% reduced rate, not the standard 20%. The zero rate covers the panels, inverter, mounting and battery storage when installed as an energy-saving measure in residential accommodation. So the price ranges above already assume 0% VAT; from 1 April 2027 expect quotes to add 5%. The detail, including the buildings that qualify, is in our guide to 0% VAT on solar panels. Source: gov.uk VAT Notice 708/6.
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Get My Free Quotes →Solar system size and cost: frequently asked questions
How much does a 4kW solar system cost in the UK?
A 4kW solar system typically costs between £5,500 and £7,000 fully installed, including panels, inverter, mounting and labour, at the current 0% VAT rate. For comparison, the Energy Saving Trust's UK-wide benchmark is a slightly larger 4.5kWp system at around £7,600, a figure that averages in difficult roofs and access. A straightforward south-facing pitched roof should sit at the lower end of the range.
How many solar panels is a 4kW system?
A 4kW system is usually about 9 to 11 panels, depending on their wattage. With 450W panels you need roughly 9, and with older 375W panels closer to 11. As a rule of thumb, each panel takes around 2 square metres of roof, so a 4kW array needs about 18 to 22 square metres of usable, well-oriented roof space.
How much roof space do I need for solar panels?
Allow roughly 2 square metres per panel. A 3kWp system needs around 14 to 16 square metres, a typical 4.5kWp system needs 20 to 30 square metres, and a 6kWp system needs about 28 to 32 square metres. Only roof faces that get decent sunlight count, so a shaded or heavily north-facing pitch does not add to your usable space.
What size solar system do I need for my home?
Work from your annual electricity use rather than your roof size. Find your yearly kWh figure on a bill, then match it to a system that generates a similar amount: around 4kWp to 4.5kWp suits a home using about 3,500 kWh a year, while a household using 5,000 kWh or running an EV and a heat pump leans towards 5kWp or 6kWp. The best size is the one where you use most of the power yourself.
Does a bigger solar system cost less per kWp?
Usually, yes. Fixed costs such as scaffolding, labour and the grid connection are spread across more panels, so the cost per kWp tends to fall as the system gets bigger. A 6kWp system costs more in total than a 3kWp one but less per unit of capacity. That does not mean bigger is always better value, because the extra output only pays back if you use or store it rather than exporting it at the lower Smart Export Guarantee rate.
Is a 3kW or 6kW system better?
Neither is better in the abstract; it depends on your roof and your usage. A 3kW system is the cheapest way in and suits a smaller home or lower daytime use. A 6kW system suits a large home with an EV or heat pump and high daytime demand. Fitting a 6kW system to a household that exports most of its output pays back more slowly than a well-matched 4kW one, so size to your consumption, not your ambition.